Cathode structure for thermionic devices



Aug. 29, 1933. I o. w. PIKE CATHODE STRUCTURE FOR THERMIONIC DEVICES Driginal Filed Oct. 9, 1930 Ihventov;

' Otis'W. Pike, by.

His Atcovneg Patented Aug. 29, 1933 PATENT OFFICE 7 1,924,375 7 I a, oA'rnonE STRUCTURE FOR TH RMIONIC" DEVICES Otis w. Pike, Schenectady, N. 1., assignor' to General Electric Company, a corporation of New York Application October 9, 1930, Serial No.l4s7,541 Renewed Apri1'27,=1933 i 5 Claims. (01. 250-215;)

The present invention relates to electrical discharge-apparatus and more particularly to thermionic devices of the power type.

The Hull Patent No. 1,790,153, granted Jan. 27, 1931, and entitled Electrical discharge devices and method of operation, also the Hull application'Serial No. 487,533',"filed Oct. 9, 1930, and entitled Cathode structures for thermionic devices both assigned tothe same assignee as r the present invention, describe and claim various forms of cathode structures for electrical discharge apparatus of the arc type.

'In arc dischargedevices which contain ther .mionic cathodes, the latter are usually indirectly heated. and employ a heater positioned within a metallic member which" serves as the cathode proper. The heater ordinarily consists of a filament wound as a spiral and protected from positive ion bombardment by the surrounding metallic member; Devices of the arc type contain an appreciable amount of gas or vapor at a pressure sufiicient to support an arc-like discharge at the impressed potentials and have a negative Volt-ampere characteristic in which the 1 current is nearly independent of the voltage. The amount of current a tube'can carry is a function of the electron emission from the cathode which for a given emission per unit area depends upon the total cathode area. It is therefore desirable in the case of large current output to provide the cathode with the greatest amount of electron emitting surface at the same time with the minimum bulk or metal content in order to facilitate heating thereof by avoiding excessive heat radiation.

The applications referred to, describe several structures in which the cathode area is increased without unduly increasing its mass and among these forms there is a type in which the cathode is provided with discs or transverse vanes coated with electron emitting material. These discs are welded or otherwise permanently secured to the metal casing and it has been found that cathodes of this construction, while practical,

are nevertheless not adapted'to quantity production and assembly. Furthermore, I the weld betweenthe vanes and the casing not only causes a fairly largetemperature drop at the joint dur-' ing operation but also precludes disassembly of the cathode when occasion requires.

An object of'the present invention is to improve the construction of indirectly heated cathodes for power tubesyparticularly with regard to eliminating the necessity for the weld referred to and to offering greater ease of manufacture,

readily be taken apart to stitution of parts.

assembly and disassembly. This object is attained in brief by providing the discs with a conflanges when assembled form a cylinder which" displaces the usual metal member of the prior art cathodes. The improved cathode assembly may be held rigidly together by bolts and can enable repairs or sub- Otherobjects and features will be apparent as the specification is perusedinconne'ction with the accompanying drawing in which Fig.1 represents an elevational view of a tube provided with a cathode improved in accordancewith my invention; Fig. 2 is an enlarged view in section of the improved cathode, while'Fig. 3 shows a representative pair of cathode discs.-

Referring toFig. l, numeral l designates the envelope ofan' electric discharge device which terminates in reentrant stems'2, 3. The upper stem 2 as shown, is closed by an inverted stemv and press 4 which terminates in an open-ended skirt portion 5." The interior of the latter has a transverse partition 6 provided with a tubular member- 7 to exclude glow discharge from the region of the press. A cylindrical control or grid inemben 8 fabricated preferably of per forated oxidized nichrome or other suitable metal," is fitted tightly'over the skirt portion figuration such that flanges and recesses are and rigidly secured thereto by a screw clamp forming in the annular space between the reentrant stem 2 and the interior of ,the envelope. Within the control member, there is a cylindrical graphite anode (not shown) secured in place by a rod 15 which is sealed in the stem 4.

The cathode 16 issu pported by a plurality of channels 17 welded toa clamp 18' which tightly embraces 1 the stem; 3. There are I two heat shields l9 aflixed to the channels. The cathode illustrated in Figil is shown in 'en-' larged" detail in Fig. 2. The heater member '20 may consist of tungsten and be woundas a spiral on a rod 21' of insulation, for example alumina (A1203), these members being shown end of thegrid remote from the skirt portion inders are closed by metal covers 30, :the low-" ermost of which has riveted thereto a pair of flexible cables 31 which 'arejoined to stiff wires 32 sealed in the press 3. A similar combination 31 and 32 of flexible and stiff leads may be taken from the lower end of the heater member. The lower end of theinsulator 21 rests on a block 33 of insulation, for example glass, to which it is anchored by a wire 34 which is hooked at one end around the glass insulator and at the other end is secured to the hub member 22. This wire constitutes a strengthening core for the insulator support 21 The block 33 which passes through aligned openings in several of the covers 30, '-rests on the lowermost cover and has apertures therethrough to ac commodate the wire 34, also the lead-in wire for the heater member. Inasmuch as the up-, per end of the heater member isattached to the member 22, the casing 28 and its associated leads serve as the 'otherlead-in conductor for the heater.

The cathode proper consists of a plurality of metal discs 35, such as shown in Fig. 3, of any suitable metal. 'These discs have a large cir-- cular opening 36 atthe center and. are provided around the opening with a pair of upset flanges 37 and 38 of different diameters, as a stepped configuration. The diametral sizes of the flanges are such that the smaller flange 37 of one disc fits snugly within the larger flange 38 of the adjacent disc and the shoulder formed between the flanges of each disc serves as a seat for the larger flange of the upper adjacent disc. While I prefer this particular type of flange, it will be understood that the term upset flanges used herein is sufiiciently broad to. include all forms and configurations of upstanding members secured to or integral with any portion of the respective discs for the specific purpose of permitting the discs to engage one another and to form a casing for receiving the heater. The

. discs are also provided with threesmall holes 39 so that when the discs are fitted together bolts i 40 may be passed through the members securely ode may be coated, if desired, with an electron V emitting substance such as barium carbonate (BaCOs).

It will be noted that the flanged portion of *zthe discs, when assembled, form a cylinder or casin the thickness of which is no greater than twicejthe thickness of the disc and hence, does not detract from the thermal efliciency of the cathode. Moreover, the casing is constituted of the metal which forms the discs and there is This flange supports a pluno necessity for welds or other form of joint which may cause loss in temperature between these members. The flanged portions may be produced readily by any suitable and well known forming process, on a quantity production basis, as may also the various parts of the cathode including the spacers 41. The structure as a Whole may be readily 'assembledand disassembled when repairs are necessary because of the absence of welding or other permanent joint The bolts 40 and the interlocking flanges cothat a cathode provided with laterally extend-- ing discs gives adequate electron emission for an exceedingly large current. Furthermore, the inoperate to make thecathode a rigid self-sup crease in electron emitting surface in the im-} proved cathode over the prior artcathodes is attained without unduly increasing its mass or metal content so that the time taken by the cathode in reaching its normal operatingtemperature is not unduly long.

Broad claims to the hollow or cavity cathode construction disclosed herein appearv in the copending application of A. W. Hull, Serial No. 156,713, filed December 23, 1926 (see British Patent No. 282,766) That application also con ting surface appear in the Hull and Ruggles application," Serial No. 268,976, filed April 10, 1928. The claims in the present application, therefore, are limited to improvements over the inventions described and claimed in the applications referred to above.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A cathode for an electric discharge device comprising a casing and a plurality of metal discs provided with upset flanges adapted to fit within one another and when assembled to form entirely said casing, and a filamentary heater member positioned within said casing.

2. A cathode for an electric discharge device comprising a casing and a filamentary heater member enclosed within the casing, a plurality.

of discs extending outward from said casing, the

latter being formed entirely from the material of the discs and being integral therewith 3. A cathode'ior an electric discharge device comprising a casing and a plurality of metal discs provided with upset flanges adapted to fit within one another and when assembled to form entirely said casing, means for spacing and locking the disc's together to form a rigid, self-supporting structure, and a filamentary heater member positioned within said casing.

, 4. A cathode for an electric discharge device comprising a casing and ,a plurality of metal discs provided with upset flanges adapted to fit within one another and when assembled to form envelope which contains inert gas at a pressure suflicient to support anarc-like discharge at the impressed voltages, a cathode and anode, an electric control member surrounding the anode, v

and a metallic member extending from said control member into the region of the cathode to reduce the voltage necessary for starting the device.

o'rrs w. PIKE." 

